Nematodes are important plant pests which cause millions of dollars of damage each year to turf grasses, ornamental plants, and food crops. Efforts to eliminate or minimize damage caused by nematodes in agricultural settings have typically involved the use of soil fumigation with materials such as chloropicrin, methyl bromide, and dazomet, which volatilize to spread the active ingredient throughout the soil. Such fumigation materials can be highly toxic and may create an environmental hazard. Various non-fumigant chemicals have also been used, but these too create serious environmental problems and can be highly toxic to humans.
The accepted methodology for control of nematodes afflicting animals has centered around the use of the drug benzimidazole and its congeners. The use of these drugs on a wide scale has led to many instances of resistance among nematode populations (Prichard, R. K. et al. [1980] "The problem of anthelmintic resistance in nematodes," Austr. Vet. J. 56:239-251; Coles, G. C. [1986] "Anthelmintic resistance in sheep," In Veterinary Clinics of North America: Food Animal Practice, Vol 2:423-432 [Herd, R. P., Eds.] W. B. Saunders, New York).
A small number of research articles have been published concerning the effects of .delta.-endotoxins from B. thuringiensis species on the viability of nematode eggs. See, for example, Bottjer, Bone and Gill ([1985] Experimental Parasitology 60:239-244); Ignoffo and Dropkin (Ignoffo, C. M., Dropkin, V. H. [1977] J. Kans. Entomol. Soc. 50:394-398); and Ciordia, H. and W. E. Bizzell ([1961] Jour. of Parasitology 47:41 [abstract]). Several patents have issued describing the control of nematodes with B.t. See, for example, U.S. Pat. Nos. 4,948,734; 5,093,120; 5,281,530; 5,426,049; 5,439,881; 5,236,843; 5,322,932; 5,151,363; 5,270,448; 5,350,577; 5,667,993; and 5,670,365.
The pesticidal activity of avermectins is well known. The avermectins are disaccharide derivatives of pentacyclic, 16-membered lactones. They can be divided into four major compounds: A.sub.1a, A.sub.2a, B.sub.1a, and B.sub.2a ; and four minor compounds: A.sub.1b, A.sub.2b, B.sub.1b, and B.sub.2b.
The organism which produces avermectins was isolated and identified as Streptomyces avermitilis MA-4680 (NRRL-8165). Characteristics of the avermectin producing culture and the fermentation process are well documented and known to those skilled in the art (Burg, R. W. et al. [1979] "Avermectins, New Family of Potent Anthelmintic Agents: Producing Organism and Fermentation," Antimicrob. Agents Chemother. 15(3):361-367). The isolation and purification of these compounds is also described in U.S. Pat. No. 4,310,519, issued Jan. 12, 1982.
Another family of pesticides produced by fermentation are the milbemycins, which are closely related to the avermectins. The milbemycins can be produced by a variety of Streptomyces and originally differed from the avermectins only in the C-13 position. The milbemycins and their many derivatives are also well known to those skilled in the art and are the subject of U.S. patents. See, for example, U.S. Pat. No. 4,547,520.
While the avermectins were initially investigated for their anthelmintic activities, they were later found to have other insecticidal properties, although the degree varies. The activity of avermectins must generally be determined empirically.
22,23-dihydroavermectin B.sub.1 is a synthetic derivative of the avermectins and has been assigned the nonproprietary name of ivermectin. It is a mixture of 80% 22,23-dihydroavermectin B.sub.1a and 20% 22,23-dihydroavermectin B.sub.1b. Ivermectin has been tested on a variety of laboratory and domestic animals for control of nematodes, ticks, and heartworms.
Avermectin B.sub.2a is active against the root-knot nematode, Meloidogyne incognita. It is reported to be 10-30 times as potent as commercial contact nematicides when incorporated into soil at 0.16-0.25 kg/ha (Boyce Thompson Institute for Plant Research 58th Annual Report [1981]; Putter, I. et al. [1981] "Avermectins: Novel Insecticides, Acaracides, and Nematicides from a Soil Microorganism," Experientia 37:963-964). Avermectin B.sub.2a is not toxic to tomatoes or cucumbers at rates of up to 10 kg/ha. Avermectin B.sub.1 is a combination of avermectin B.sub.1a (major component) and avermectin B.sub.1b. It has demonstrated a broad spectrum of insecticidal activities. The data indicate that avermectin B.sub.1 is primarily a miticide, although it is also effective on the Colorado potato beetle, potato tuberworm, beet armyworm, diamondback moth, gypsy moth, and the European corn borer.
The use of avermectins in various agricultural applications has been described in publications and patents. The use of avermectin with spray oils (lightweight oil compositions) has been described. See, for example, U.S. Pat. No. 4,560,677 issued Dec. 24, 1985; EPO applications 0 094 779 and 0 125 155; and Anderson, T. E., J. R. Babu, R. A. Dybas, H. Mehta (1986) J. Econ. Entomol. 79:197-201.
Fatty acids are a class of natural compounds which occur abundantly in nature and which have interesting and valuable biological activities. The in vitro activity of fatty acids against many medically important fungi and bacteria is well known. There is a much smaller body of literature concerning the activity of fatty acids and their derivatives against pathogens on agricultural crops. Ahmed et al. (Ahmed, S. M., F. Ahmad, S. M. Osman [1985] JAOCS 62:1578-1580) report in vitro inhibition of radial growth of several fungal genera with plant pathogenic representatives. Recently there has been an expanding use of "insecticidal soaps" in agriculture which are salts of certain fatty acids. Chase et al. (Chase, A. R., L. S. Osborne [1983] Plant Disease 67:1021-1023) observed that applications of an 18:1 fatty acid salt "insecticidal soap" gave moderate preventive control of two foliage plant diseases and actually exacerbated two other diseases. Nickel and silver salts of fatty acids have been used to control pathogens on plants: GB Pat. Nos. 907,842 and 1,219,077. In U.S. Pat. No. 3,983,214, Misato et al. claim a fungicidal composition containing a sucrose fatty acid ester. In U.S. Pat. No. 4,771,571, Obrero et al. describe a method of preventing infections of pineapple by treating the fruit, while on the bush, with a surfactant. In U.S. Pat. No. 4,002,775, Kabara et al. claim microbicidal food additives comprising 1 or 2-mono-laurin polyol ester. The use of fatty acid esters and alcohols for the control of powdery mildew on apple buds has been described (Frick, E. L., R. T. Burchill [1972] Plant Disease Reporter 56:770-772; U.S. Pat. No.3,931,413). In the '413 patent, Frick et al. emphasize the phytotoxicity of fatty acids and state that the acid or salt form should only be used on dormant plant tissue. The phytotoxicity of fatty acids and their salts is well documented and has long been believed to be a barrier to the use of these compositions on living plants. See U.S. Pat. No. 5,246,716. Tarjan and Cheo (Tarjan, A. C., P. C. Cheo [1956] "Nematocidal Value of Some Fatty Acids," Bulletin 332, Contribution 884, Agricultural Experiment Station, University of Rhode Island, Kingston, 41 pp.) report the activity of certain fatty acids against nematodes. Tarjan and Cheo do not disclose or suggest the use of fatty acid esters. In 1977 Sitaramaiah and Singh (Sitaramaiah, K., R. S. Singh [1977] Indian J. Nematol. 7:58-65) also examined the response of nematodes to fatty acids. These researchers examined the effects of low molecular weight acids such as acetic, formic, propionic, and butyric acids. The results of these tests with short chain acids were equivocal, showing nematode-inhibitory action in some instances and stimulatory activity in other instances. Phytotoxicity of these acids was observed at higher concentrations. These short chain fatty acids were also examined by Malik and Jairajpuri (Malik, Z., M. S. Jairajpuri [1977] Nematol. medit. 12:73-79), who observed nematode toxicity at high concentrations of the fatty acids. In 1987, Kiuchi et al. (Kiuchi, F., N. Miyashita, Y. Tsuda, K. Kondo, H. Yoshimura [1977] Chem. Pharm. Bull. 35:2880-2886) reported the anthelmintic effect of fatty acids obtained from betel nuts. The fatty acids were found to be toxic against larvae of worms which cause parasitic diseases in humans and animals. Stadler et al. (Stadler, M., A. Mayer, H. Anke, O. Sterner [1994] Planta Med. 60:128-132) studied fatty acids and other compounds with nematicidal activity which could be obtained from cultures of Basidiomycetes. Stadler et al. primarily evaluated long chain fatty acids having, for example, 16 to 18 carbons.
Fatty acid ester compositions have been described in U.S. Pat. No. 5,284,819, but this patent does not disclose or suggest the use of fatty acid esters to control nematodes.
Furthermore, the prior art does not teach or suggest that certain fatty acid esters can be used to kill the eggs of nematodes. For example, the 1958 Stansbury patent (U.S. Pat. No. 2.852,426) is silent regarding ovicidal activity; and Tarjan and Cheo, supra, actually teach against the ovicidal properties of fatty acids.